By Alexandra FullerFrom my cabin window in Teton Valley, Idaho, real life looks like this: There is a snow-covered meadow, and beyond that a stand of bare gray aspen trees, and beyond that a spill of sun-stunned white until the Earth rears back on itself and makes the Rocky Mountains. It is a landscape that has inspired an unprecedented act of Congress and a great many acts of poetry, but I measure it by its ordinary day-to-day gifts.

Today, for instance, in early March, it is far from warm—the slipping hold of winter is still evident—and my horses hunch their shoulders to the wind, their tails swinging under their bellies. But when I take hay out to the snowburied meadow for them, a great blue heron (the first I have seen this season) startles at my approach, lumbers into the air, and careers into an icy headwind. It evokes a drunk pterodactyl. And that is gift number one.

At noon Wyoming Public Radio warns listeners that bears are coming out of hibernation and that we should beware of the hungry animals on the prowl for food. And flies, giddy with the promise of longer days, seep out of the logs of my cabin and fall in exhausted layers on the windowsills or buzz weakly over my cup before sinking to their death-by-tea. Life, in all its dangerous, complicated, annoying glory, has returned to this corner of the sun-tilted world. And that is gift number two.

Then at sundown the earth is starting to emit the sour breath of winter, which is six months' worth of accumulated manure and rotting grass, and the diminished carcass of the coyote that died under a willow bush four feet from the frozen pond in a snowdrift in January and has been picked over by magpies ever since. There is the chaos of winter debris in my yard, and out across the horses' paddock as far as I can smell, there is the life-affirming stench of renewal. And that is gift without measure.

We are being released from the deserting grip of winter. From late September until just the other day, it felt as if it were only me out here. Me and the coyotes, the black bull moose with the Elvis curl to his lip, the two bald eagles and their offspring, the ten trumpeter swans. I counted these creatures with fierce, almost possessive regularity, as if my own life depended on their surviving until the spring. But two months from now (as March and April melt into May) until the frost comes again, the casual observer could be forgiven for supposing that life is recklessly generated in these mountains.

For in the summer this area seethes with wildlife. Animals spill with exuberant abandon onto land we humans think of as private and that deer and elk think of as forage. The greatest concentrations of animals spend their summers in the protected confines of the proximate national parks—Yellowstone and Grand Teton—which, in their turn, give a teasing impression of plenty. There are very few places left in North America, less than a handful, that still contain the number of species that existed when Europeans first explored and settled the continent. This is one of them. John Colter (of the Lewis and Clark expedition) walked through this region in 1807. Nearly 200 years later, almost every species of animal life that he could have seen can still be seen today. Within Grand Teton alone there are, in the fat months of summer, 18 species of carnivores (including wolverines, wolves, and black and grizzly bears), 7 native species of hoofed mammals, 22 species of rodents, 6 of bats, 5 of amphibians, 16 of fish, more than 300 species of birds, 900 species of flowering plants, and 7 species of conifers.

But this country is sliced into two worlds. The brittle paucity of winter is one world; the careless glut of summer is the other. The bridge between the two worlds is a series of ever diminishing migration routes that take the animals and birds by earth and air from summer in and around Yellowstone and Grand Teton National Parks to winter lands near and wide. As Jackson-based biologist Franz Camenzind told me, "If you look at where some of Yellowstone and Teton's widest ranging species go—there are Swainson's hawks and hummingbirds that go all the way to Central and South America —you could argue that the influence of those two parks extends beyond our national borders. This is a very impressive reservoir of animals we have here, but they couldn't survive if they were limited to the parks' boundaries."

A capricious act of God, or an act of supreme human carelessness, could quite easily remove the forces of life from this landscape. Even so, even without its wildlife, the hard, inorganic matter that remains would still make for ravishing visions because this landscape aches with a beauty that is young and correspondingly restless. So startled and inspired were our forefathers by this picturesque range of geography that they took the novel step, in 1872, of declaring in an act of Congress that Yellowstone be set aside as the world's first national park, "for the benefit and enjoyment of the people." In 1950 Grand Teton National Park, as we know it today, was created, a 310,000-acre (125,000-hectare) tract of managed wildlands that runs along the spine of the Rocky Mountains and into the valley of Jackson Hole.

Together, these two national parks (linked by the John D. Rockefeller, Jr., Memorial Parkway) constitute over 2.5 million acres (1.01 million hectares), each acre tumbling upon itself to rival the last acre of beauty. Within a space that can be covered on my map by the tip of one finger, forests, mountain ranges, geysers, mud pots, and river valleys congregate in a surfeit of scenery. It is as if the vertigo-inducing flats of the American Midwest toppled to a halt right here and made up for the relatively bland expanse of the prairies with more than ordinary remorse.

Here is how this uneasy scenery was born: About 13 million years ago there was a time of great violence, and a series of immense earthquakes, separated by pauses of about two thousand years, ripped along a fault found where the Teton Range now meets the valley floor. By 12,000 years ago glaciers had carved canyons through the resulting uplift and created a sequence of stark, steep-flanked peaks, the tallest of which, the Grand Teton, surges well over a mile above the sagebrush flats into the sky. Conceived in even greater violence, Yellowstone's central plateau was born in a succession of massive volcanic eruptions, the last of which occurred some 600,000 years ago.

It is beautiful. But no one could accuse it of being kind. The ground here is inhospitable, and not just around Yellowstone's geysers, where the crusty earth evokes the hostile and sulfurous cauldrons of Hades. Even grassy meadows are, on closer inspection, sewn onto a fragile scuff of the planet's surface. Soils created by volcanic activity in Yellowstone's higher elevations tend toward parched austerity, and the rocky slopes of Grand Teton are severe and exposed. The growing season in the subalpine forests is stingy—about two months, extending to a hardly generous three or four months in the valley bottoms. By mid-September the air takes on a deadened, bitter scent, and a settling silence mantles the earth. Yet pressed out by the greater stretches of human development that have devoured their habitat, wildlife has found a home in these unfavorable climes. And it is the wildlife that continually reinvents the scenery: grazing and nesting, birthing and hunting, giving its canyons and meadows subtly new forms. Pull tightly enough on the thread of one creature's habits, and a whole ecosystem can pitch down on top of you. It is as John Muir said, "When we try to pick out anything by itself, we find it hitched to everything else in the universe."

Grand Teton and Yellowstone's boundaries were originally determined by the extent of their scenic values, but it was not until the last half of the past century that anyone thought to try to define the boundaries of the parks not in terms of absolute square miles but in terms of the range taken by the wildlife that use the parks and for which the parks are increasingly important. In the 1970s two biologists, John and Frank Craighead, determined to comprehend Yellowstone and Grand Teton National Parks not as explained by humans who understand acres and fences and geopolitical units but as experienced by grizzly bears that roam with their own set of rules, often at odds with the agenda of mankind. The Craigheads were the first to draw significant attention to the idea that if the diversity and quantity of wildlife within the parks were going to outlive the century, then it was not enough to draw a line around a selection of animals and their summer range, as if they were immobile scenery, and call it protected. The survival strategies of the wildlife and the systems on which they depend (migration and access to winter ranges, for example) have to be managed too.

If Yellowstone and Grand Teton were going to continue to host not only grizzly bears (those great symbols of freedom and bad temper) but also pronghorn (whose yearly journey from Grand Teton to the Upper Green River Valley is the longest overland mammal migration between the Canadian border and Tierra del Fuego), then there would have to be porous park borders. There would have to be a stain of lands beyond the limits of the national parks in which bears could roam and into which pronghorn could pass the thin, cold months of winter.

The all-important bridge between the worlds of winter and summer consists, largely, of public land beyond the parks' borders and has been dubbed the Greater Yellowstone Ecosystem (GYE). Anyone intimate with the ecosystem accepts that its boundaries are more or less arbitrary. For instance you might argue, based on migrating hummingbirds, that the GYE should extend down to Central and South America. But that's not a practical chunk of land to bite off. Franz Camenzind, the Jackson biologist, told me, "In the end, for sanity's sake, you have to draw a line in the forest and call it an ecosystem."

No longer defined just by the range needed to accommodate the grouchy travels of Ursus arctos horribilis, the GYE as a concept has expanded to also include (for instance) intact watersheds and mountain ranges. This spread of approximately 18 million acres (7 hectares) now swallows, in addition to the two national parks, more than a dozen towns, all or most of seven national forests, three national wildlife refuges, more than twenty other state and local jurisdictions, as well as numerous ranches, roads, and oil and natural gas fields in Idaho, Wyoming, and Montana. Grand Teton and Yellowstone National Parks are at the heart of the GYE, and the GYE is the body supported by the parks. Without one or the other, the wildlife would cease to exist, and both would be reduced to a state of life-starved scenery.

From my cabin I can drive across the GYE in any direction in a day. "The GYE," said Camenzind, "is the largest relatively intact ecosystem in the lower forty-eight, but when you look at it on a map, or fly over it, it's tiny. It's the largest we have, but it's not large."

Because of its reduced scale, we humans who attempt to manage the GYE's survival need to pay attention not just to the celebrity species (grizzlies, wolves, bison) but to the quieter processes that speak of the wildlife's ability to survive the caprices of our desires. We have to try to put ourselves in the hooves of the animals we want to live with.

Joel Berger is lean and weather-washed and unassuming, a man whose mind is bilingual between the human world and the world of animals. For the past nine years he has endured charging moose, surprised bears, the hostile breath of Rocky Mountain winters, and long trudges through leg-grasping sagebrush in pursuit of freshly delivered moose droppings. As a biologist with the Wildlife Conservation Society, he has been studying what effect, if any, the recent reintroduction of wolves into the GYE is having on the resident moose population, which had not known wolves for generations. Berger has analyzed the fertility of moose cows (hormones present in droppings indicate pregnancy rates) and the subsequent calf survival rate and has tested moose reaction to recorded wolf calls as well as other natural sounds. This has led him to conclude that a recent drop in the moose population is due not to the presence of wolves, as was commonly supposed, but to the drought that has desiccated the area for the past four years. In these lean times fewer cows conceive, and fewer calves survive the crucial crunch of summer before the deadening of winter.

The day after winter solstice, Berger and I set out walking across the sagebrush flats at the south end of Grand Teton National Park. A collared cow moose was lying with four males and one other female in the pale green scrub. When we were almost upon her, Berger suddenly cupped his hands and called like a raven. The cow moose didn't flinch. Then he howled like a wolf. The cow moose looked bored. "When they've had calves taken by wolves, they respond to that call," Berger said. "It doesn't take them long to learn that lesson when it's directly affected them. But they don't seem to have an ancestral memory of wolf predation." The moose delivered her sample, and Berger carefully scooped it into a Ziploc bag, keeping a wary eye on the cow herself, who had moved casually off toward one of the males, just beyond kicking distance. We trudged back to the road, turning our backs on the wintering moose. "I've been doing this all my working life because I'm curious what impact we have on the natural world." He smiled into the pale winter sun. "But what's almost as curious—and perhaps harder to quantify—is the impact the natural world has on us."

I think I know. How lonely it would be to stare down a long winter—however rewarding the scenery—without the predictable companionship of moose, coyotes, magpies, swans. How disheartening to miss the prospect of a noisy spring as heralded by the raucous trilling of a red-winged blackbird, the shy pulsing of a hummingbird at the sugar feeder, the startling rush of ducks off the rivers, or the uncurling of a spindly elk fawn from behind a fallen aspen.